Wide databus architecture

ABSTRACT

A dynamic random access memory (DRAM) having pairs of bitlines, each pair being connected to a first bit line sense amplifier, wordlines crossing the bitlines pairs forming an array, charge storage cells connected to the bitlines, each having an enable input connected to a wordline, the bit line sense amplifiers being connected in a two dimensional array, pairs of primary databuses being connected through first access transistors to plural corresponding bit line sense amplifiers in each row of the array, apparatus for enabling columns of the first access transistors, databus sense amplifiers each connected to a corresponding data bus pair, a secondary databus, the secondary databus being connected through second access transistors to the databus sense amplifiers, and apparatus for enabling the second access transistors, whereby each the primary databus pair may be shared by plural sense amplifiers in a corresponding row of the array and the secondary databus may be shared by plural primary databus pairs.

RELATED APPLICATION(S)

This application is a Continuation of application Ser. No. 11/476,422,filed Jun. 28, 2006, which is a Continuation of application Ser. No.10/691,111, filed Oct. 22, 2003, now U.S. Pat. No. 7,095,666, which is aContinuation of application Ser. No. 10/278,195 filed on Oct. 22, 2002,now U.S. Pat. No. 6,661,723, which is a Continuation of application Ser.No. 10/056,818 filed on Jan. 24, 2002, now abandoned, which is aContinuation of application Ser. No. 09/761,297 filed on Jan. 16, 2001,now U.S. Pat. No. 6,366,491, which is a Continuation of application Ser.No. 08/986,358 filed on Dec. 8, 1997, now U.S. Pat. No. 6,195,282, whichis a Continuation of application Ser. No. 08/226,034 filed on Apr. 11,1994, now U.S. Pat. No. 5,742,544. The entire teachings of the aboveapplications are incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to the field of integrated semiconductormemories, and in particular to the structure of a very large dynamicrandom access memory (DRAM).

BACKGROUND OF THE INVENTION

A semiconductor DRAM is typically comprised of parallel pairs ofbitlines crossing wordlines. A charge storage cell is located adjacentintersections of the bitlines and wordlines, each cell being comprisedof a charge storage capacitor connected for access to a bitline througha cell access field effect transistor (FET), which FET is enabled from awordline. Each bitline pair is connected to a sense amplifier, which isconnected via an access transistor, enabled by a Y-decoder, to adatabus. The databuses are located on the chip in parallel to thewordlines and parallel to a strip of associated sense amplifiers, andorthogonal to the bitlines. Read and write amplifiers are connected tothe databuses.

As the capacity of DRAMs increases, it becomes increasingly important tominimize the size of the chip in which it is integrated, in order toincrease yields and to decrease the cost per bit of the DRAMs.

SUMMARY OF THE INVENTION

The present invention is a DRAM structure which significantly decreasesthe physical space used on a chip for a given size of DRAM, and at thesame time provides a structure that can accommodate a significantlyincreased memory capacity for a given chip size. It can provide widerdata buses providing greater bandwidth which is useful for applicationspecific memories (ASMs) or embedded memories in ASIC devices. In suchan application a wide databus could be used directly without furtherdecoding, since data need not go off-chip which is limited by the numberof pins on an integrated circuit chip package. The present inventionavoids the requirement for separate databuses for each strip of senseamplifiers, but instead connects two or more sense amplifiers indifferent strips to primary databus pairs, and the databus pairs,through databus sense amplifiers, to a secondary databus whichpreferably runs in parallel to columns of the DRAM. Strips of bit linesense amplifiers are connected to the primary databus through accessFETs which are enabled by a column array select signal.

The databus sense amplifiers are connected to the secondary databus bysecond access transistors, which may be enabled by Y-decoders. Indeedadditional databus sense amplifiers may be connected in parallel throughisolation FETs to the primary databuses and to the second accesstransistors. With enabling or inhibiting of the isolation FETs,selectable columns of databus sense amplifiers may be enabled, wherebythey may be used as page caches, storing pages of databits for writingto or having been read from columns of storage cells.

Thus the primary databuses are shared among many arrays. Since pluralparallel databuses each associated with a column of bit line senseamplifiers are not required, significant chip space is saved. Thedatabus sense amplifiers can serve as caches, and in the plural paralleldatabus sense amplifier embodiment, the databus sense amplifiers canhold multiple pages of data in cache.

In accordance with an embodiment of the invention, a DRAM is comprisedof an array of bitline sense amplifiers, columns of said bitline senseamplifiers being selectable by array select signals for application ofcharge between a selected column of bitline sense amplifiers andcorresponding primary databus pairs, whereby each row of bitline senseamplifiers shares the same primary databus pair, and further comprisingdatabus sense amplifiers for application of charge between a databuspair and a secondary databus.

In accordance with another embodiment, the DRAM described above furtherincludes plural databus sense amplifiers connected in parallel throughisolation apparatus to each primary databus pair and apparatus forenabling and inhibiting columns of the plural databus sense amplifierstogether to connect and disconnect the columns of the plural databussense amplifiers to corresponding databus pairs, whereby selectablecolumns of the plural sense amplifiers may be connected to the primarydatabus pairs.

In accordance with another embodiment of the invention, a dynamic randomaccess memory (DRAM) is comprised of pairs of bitlines, each pair beingconnected to a bit line sense amplifier, wordlines crossing the bitlinepairs forming an array, charge storage cells connected to the bitlines,each having an enable input connected to a wordline, the bit line senseamplifiers being connected in an array, pairs of primary databuses beingconnected through first access transistors to plural corresponding bitline sense amplifiers in each row of the array, apparatus for enablingcolumns of the first access transistors, databus sense amplifiers eachconnected to a corresponding data bus pair, a secondary databus, thesecondary databus being connected through second access transistors tothe databus sense amplifiers, and apparatus for enabling the secondaccess transistors, whereby each primary databus pair may be shared byplural sense amplifiers in a corresponding row of the array and thesecondary databus may be shared by plural primary databus pairs.

In accordance with another embodiment, the DRAM described above furtherincludes plural databus sense amplifiers connected in parallel throughisolation apparatus to each primary databus pair and to the secondaccess transistors, and apparatus for enabling and inhibiting columns ofthe plural databus sense amplifiers to connect and disconnect thecolumns of the plural databus sense amplifiers together to correspondingdatabus pairs, whereby columns of the plural sense amplifiers may beconnected to and sense the corresponding databus pairs.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the invention will be obtained by reading thedescription of the invention below, with reference to the followingdrawings, in which:

FIG. 1 is a diagram of part of a DRAM in accordance with the prior art,

FIG. 2 is a diagram of part of a DRAM in accordance with a preferredembodiment of the present invention,

FIGS. 3A and 3B are timing diagrams used in illustrating reading andwriting in the preferred embodiment,

FIG. 4 is a diagram of part of the DRAM in accordance with anotherembodiment of the present invention, and

FIG. 5 is a diagram of part of a DRAM illustrating two additionalembodiments of the invention.

FIG. 6 illustrates a parallel connection of sense amplifiers to theprimary databus.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, in a prior art DRAM bit line pairs 1 are connectedto bit line sense amplifiers 3. Word lines 5 cross the bit lines, andcharge storage cells comprised of charge storage capacitors 7 in serieswith cell access transistors 9 (FETs) are located adjacent theintersections of the wordlines and the bit lines. The transistors 9 areenabled by the adjacent word lines 5.

The sense amplifiers are connected to databus lines 11 via databusaccess transistors (FETs) 13. FETs 13 are enabled from the outputs ofY-decoders 15. Read amplifiers 17 and write amplifiers 18 are connectedto the databus lines 11.

As is well known, data arriving on the databus via the write amplifiersare sensed by the sense amplifiers and full logic level of the data isapplied to the bit lines 1. Upon enabling of FETs 9 from one of the wordlines, charge on the associated bit lines is passed through the FETs tothe charge storage capacitors, thereby completing a write cycle.

To perform a read cycle, a sense amplifier is enabled, a bit line pairis precharged, and a logic level is applied to a word line. An FET isthereby enabled, allowing the charge on a cell capacitor to be dumped tothe associated bit line. The sense amplifier senses the charge, restoresfull logic level into the cell and drives the databus. The resultingsignal on the databus is passed through a databus read amplifier.

An embodiment of the present invention is illustrated in FIG. 2. Thedatabus 11 of FIG. 1 is now referred to as a secondary databus 11, towhich read and write amplifiers 17 and 18 are connected as in the priorart. However, access to databus 11 is made not directly from the senseamplifiers, but from primary databus pairs 19. The primary databus pairs19 run in rows, each pair preferably on opposite sides of a row of bitline sense amplifiers 3. In one embodiment, each of the primary databuspairs 19 is connected to a pair of lines of the secondary databus 11 viaa databus sense amplifier 21. The structure of the databus senseamplifiers is similar to a bit line sense amplifier; one will be shownand described in schematic form in FIG. 4. Each databus sense amplifieris connected to a primary databus pair, and via a pair of second accesstransistors 23 to a pair of lines of secondary databus 11. In thismanner opposite polarity logic pairs of primary databuses DBO, /DBO,DB1, /DB1 may be connected to opposite polarity logic pairs of secondarydatabus lines IBO, /IBO, IB1, /IB1.

A Y-decoder 25 is connected to the gates of second access FETs 23connected to each pair of databus sense amplifiers 21 connected toopposite logic pairs of primary databuses. Read amplifiers 17 and writeamplifiers 18 are connected to each pair of secondary databus lines 11.

Each bit line sense amplifier is connected to a primary databus pair 19,which run in parallel to the bit lines, through primary databus accesstransistors (FETs) 27. FETs 27 connected to bit line sense amplifiers 3in a column have their gates connected together and to an array selectlogic line 29, i.e. Array Select 0, Array Select 1, etc., eachassociated with an array of charge storage cells 7 enabled by a group ofword lines.

Consider now FIGS. 3A and 3B to understand operation of the embodimentshown in FIG. 2. To read data stored in the charge cells, a word line 5(WL) is first enabled. The charge stored in the memory cell istransferred to the bitline, and then at the time indicated as “bit linesensing,” the bit lines are sensed by bit line sense amplifier 3. Thebit lines 1 (BL, /BL) are rapidly charged to full logic level.

Following sufficient time to charge, a logic signal is applied to anarray select line 29 (e.g. Array Select 0) for an interval, whichenables FETs 27. Once FETs 27 are conductive, the databus pair 19 beginsto charge slowly from the bit lines. The databus pair is then sensed bythe databus sense amplifier 21, resulting in rapid increase of thedatabus pair voltage to full logic level (DB /DB).

In this way the data stored in an entire array of bitline sense amps,representing many thousands of bits in a modem DRAM, can be transferredto an array of databus sense amplifiers in a single operation.

With application of an address to Y-decoder 25, addressing FETs 23, thelogic levels on selected databus pairs are transferred to pairs of linesof the secondary databus 11, for reading by read amplifier 17.

To write to the memory (FIG. 3B), opposite polarity logic levels arewritten to the secondary databus pairs by write amplifiers 18 (DB, /DB).The databus sense amplifiers 21 are enabled by Y-decoder 25 receivingand decoding an address signal. With enabling of the sense amplifiers,the logic levels on the secondary databus are sensed, and the logiclevels (DB, /DB) of the databus pairs 19 are brought to full logiclevel.

A logic signal is then applied to a word line (WL), followed by enablingof the primary databus access FETs 27 by an array select signal. Thecharge on the associated databus pair 19 slowly rises, followed bysensing by the bit line sense amplifier 3. The bit line pair voltagethen rapidly changes to opposite polarities of full logic level on eachbit line of the pair (BL, /BL). With the word line selected, the cellaccess FETs 7 are enabled, and the charge on each bit line passesthrough the associated cell access FET to its cell capacitor, forstorage.

It may thus be seen that the primary databuses are shared by manyarrays, thus saving significant chip area, since the databuses of theprior art (analogous to the secondary databus of this embodiment) arenot required in each array.

It should be noted that the secondary databus may be located as acentral spine in the DRAM, with primary databuses leading orthogonallyin orthogonally opposite directions therefrom, and the DRAM arraysdisposed in mirror image on both sides of the spine. There may be twoseparate parallel secondary databuses, or both may share the samesecondary databus in a time shared manner. Sharing of a secondarydatabus by two mirror image DRAM arrays is possible by simply addressingthe Y-decoders to control which primary databus pair of which DRAM arrayhas access to the secondary databus at a particular time.

In accordance with another embodiment, plural databus sense amplifiersare connected in parallel to each bit line pair, but each isolated fromthe bit line pair by an isolation device such as an FET.

A databus sense amplifier suitable for parallel connection as shown inFIG. 6 is shown in FIG. 4. A pair of FETs 31 of one conductivity typeeach has its gate connected to a corresponding FET of a pair of FETs 33of opposite conductivity type. The gate of one of the FETs of oneconductivity type is connected to one databus DB of the databus linepair through an optional isolation FET 35, and the gate of the other ofthe FETs of the one conductivity type is connected to the otherdatabus/DB of the databus pair through a similarly optional isolationFET 35. The FETs 35 are enabled (made conductive) by an /ISOLATION logiclevel applied to their gates.

In operation, any column of databus sense amplifiers may be used byapplying an /ISOLATION logic level to the gates of FETs 35, while anISOLATION (inhibit) logic level is applied to the gates of FETs 35 ofall other columns of databus sense amplifiers. This provides means forselection of which sense amplifiers are used to sense the bit line pairsin a read operation or the secondary databus for application of datalogic levels to the bit line pairs in a write operation. Since eachsense amplifier stores the logic level of a bit, each strip of senseamplifiers can store a page of bits, and by enabling each column ofsense amplifiers, multiple pages of bits may be stored in cache. Thisallows thousands of bits to be transferred in a single operation tocache registers.

Additional embodiments are shown in FIG. 5. In this embodiment insteadof databus pairs 19 being shared by a single row of bit line senseamplifiers, databus pairs 19 are shared (multiplexed) by more than onerow of bit line sense amplifiers (two rows of bit line sense amplifiersbeing illustrated). FIG. 5 also illustrates direct databus sensing.

In respect of the latter embodiment, each databus pair 19 is connectedto the input of a read amplifier 37, 39 and to the output of a writeamplifier 38, 40 connected in parallel. No secondary databus is used,though the outputs Dout and inputs Din of the read and write amplifiersmay be connected to a central column of conductors. The primarydatabuses may be either of the form described with reference to FIG. 2,or may be multiplexed as will be described below.

The read and write amplifiers operate to read and write the primarydatabuses directly, and no Y decoder need be used.

As noted above, the primary databuses may be multiplexed by more thanone row of bit line sense amplifiers. Thus for example bit line senseamplifiers 3A and 3B, 4A and 4B, etc. share primary databuses 19.Multiplexed databuses 19 may be connected to a strip of data bus senseamplifiers 21 as shown in FIG. 2, or may be connected directly to readand write amplifiers as shown in FIG. 5.

FIG. 2 shows the bit line sense amplifiers being connected to associateddatabus 19 via FETs 27, which are enabled by an array select 0 or 1logic signal being applied to their gates. In the present embodimentthis is still the case for bit line sense amplifiers 3A and 4A, but bitline sense amplifiers 3B and 4B are connected to the databus 19 via FETs28. A separate array select logic signal is applied to the gates of FETs28, the latter being referred to as “array select 0 or 1, even,” theformer being referred to as “array select 0 or 1, odd.”

In operation, to enable the strip of bitline sense amplifiers 3A todatabus 19, an array select 0 odd logic signal is applied to the gatesof FETs 27 associated with sense amplifiers 3A. To enable the strip ofbitline sense amplifiers 4A, to access databus 19, an array select 1 oddlogic signal is applied to the gates of FETs 27 associated with senseamplifiers 4A. To enable the strip of bitline sense amplifiers 3B toaccess the databus 19, an array select 0 even logic signal is applied tothe gates of FETs 28 associated with bitline sense amplifiers 3B. Toenable the strip of sense amplifiers 4B to access databus 19, an arrayselect 1 even logic signal is applied to the gates of FETs 28 associatedwith the strip of bitline sense amplifiers 4B.

Thus the databus 19 may be multiplexed both by rows and columns of senseamplifiers.

A person understanding this invention may now conceive of alternativestructures and embodiments or variations of the above. All of thosewhich fall within the scope of the claims appended hereto are consideredto be part of the present invention.

1. An embedded dynamic random access memory (DRAM) comprising: chargestorage cells formed at intersections of word lines and complementarybit line pairs; bit line sense amplifiers for fully sensing bit linedata to full logic levels; complementary data bus pairs for transferringsaid fully sensed bit line data from said bit line pairs, said data buspairs running in a direction parallel to said bit line pairs; and readand write amplifiers coupled to said data bus pairs for reading saidfully sensed bit line data from said data bus pairs and writing bufferedinput data to said data bus pairs, respectively, with no Y-decoder. 2.An embedded memory as in claim 1 wherein said memory is embedded withinan application specific integrated circuit (ASIC).
 3. An embeddeddynamic random access memory (DRAM) comprising: charge storage cellsformed at intersections of word lines and complementary bit line pairs,said bit line pairs running in a first direction on said memory; bitline sense amplifiers for fully sensing bit line data to full logiclevels; complementary data bus pairs for transferring said fully sensedbit line data from said bit line pairs, said data bus pairs running in adirection parallel to said bit line pairs; a plurality of data busamplifiers for sensing selectable pages of data and transferring thedata to cache registers.
 4. An embedded memory as in claim 3 whereinsaid memory is embedded within an application specific integratedcircuit (ASIC).